Machines and equipment used in many production sites are typically controlled by control systems constituted by programmable controllers (programmable logic controllers, also referred to as “PLCs”, hereinafter). In such control systems, the PLC includes a CPU unit (central processing unit), and an I/O (input/output) unit, which receives signals from external switches and sensors and outputs the signals to external relays and actuators. The PLC is connected over a network to a plurality of remote I/O terminals. Each remote I/O terminal includes a communication coupler and a plurality of I/O units.
As one such control system, JP 2012-195653 A (patent document 1) discloses a network system constituted by a master device and a plurality of slave devices and a technique for detection of connection abnormalities of the slave devices. The data transmitted from the master device is returned back to the master device after being transmitted sequentially from the most upstream slave device to the most downstream slave device.
In order to support the design and construction of such control systems, software has been proposed for simulating configurations of control systems with PCs (personal computers) and setting the control systems. With this software, it is possible for designers of the control systems to consider configurations of devices (units) included in the control devices before purchasing an apparatus, and to design the control systems in consideration of the properties of the units.